Oxide cathode and method of making same



Patented Nov. 5, 1935 UNITED STATES ATENT OXIDE CATHODE AND METHOD OF MAKING SAME No Drawing. Application September 5, 1930, lsig'sial No. 479,922. In Hungary December 23,

11 Claims.

My invention refers to a new kind of oxide cathodes, such as are used for instance in electrical discharge vessels, and to the method of producing same.

In a copending application for patent of the United States Serial No. 479,921 filed September 5, 1930 a process has been disclosed for producing oxide cathodes by which the metal body serving as core of the oxide cathode is provided with a coating of tungsten oxide or molybdenum oxide, these oxides being separated from suitable solutions of tungsten or molybdenum compounds by electrolytical decomposition and depositedon the metal body arranged in the solution and inserted in the electrolytical circuit as cathode. A cathode of this kind which is coated with one of these oxides is then mounted on the support and subjected in a well known manner in the discharge vessel to the action of alkaline earth metal vapors.

The production of the coating on the metal body serving as the core of the cathode was effected with the aid of difierent kinds of solutions of tungstic or molybdic acids, for instance acidulated solutions of orthotungstates or orthomolybdates.

In accordance with the method forming an object of the present invention oxide cathodes are produced by coating the metal body serving as the core of the cathode, before the alkaline earth metal vapor is precipitated thereon, with one or a plurality of compounds of metals of high melting point which do not form alloys with the alkaline earth metal, such compounds being for instance those compounds of tungsten or molybdenum, which already contain those alkaline earth metal oxides which shall be produced on the surface of the cathode. Compounds of this kind are for instance the so-called alkaline earth metal bronzes, for instance the barium tungsten bronze BaW3O9 described under this denomination for instance by Smithell on page 38 of Tungsten (London 1926). Under the action of alkaline earth metal vapors these compounds are decomposed by reduction, there being formed besides metallic tungsten or molybdenum also the alkaline earth metal oxide. At the same time alkaline earth metal oxide is formed by the alkaline earth metal which is the" cause of the decomposition, the metal being oxidized by the oxygen in the bronze.

Thus according to the new method only part of the layer of alkaline earth metal oxide coating the cathode surface is produced by the oxidation of the alkaline earth metal precipitated on the cathode from the vapor phase, while another part is formed by decomposition of the tungsten or molybdenum bronze deposited on the cathode before the precipitation of the alkaline earth metal.

The method according to which a coating or" 5 tungsten or molybdenum bronze is produced on a metal body is disclosed and claimed in a copending application of even date and no claim is made in the present application to this process. The process consists in placing the metal body 10 forming the core of the cathode in a solution of an alkaline earth metal salt of metaor polytungstic or molybdic acid or a mixture of such salts. The metal body placed in the solution is inserted as cathode in the electrolytic circuit and 15 exposed for a short time to the action of an electric current. By electrolytic decomposition of the solution the alkaline earth metal bronze is deposited on the cathode body under the form of auniform firmly adhering layer. The adhesion 20 of the bronze layer to the core is such that the layer is not loosened when the cathode is subjected to mechanical treatment. Therefore the coating of the cathode body with the bronze layer can be efiected before fixing the cathode on its 25 support in the discharge tube.

The decomposition of the alkaline earth metal bronzes by means of alkaline earth metal is effected within the discharge vessel, an alkaline earth metal being precipitated from the vapor phase on the cathode. When the decomposition process has come to an end, the cathode is heatedto a temperature exceeding by some 100 degrees the normal temperature of operation of the discharge vessel (for instance 1500 C.) in order to make sure that the layer of alkaline earth metal oxide will firmly adhere to the cathode body.

Example 1 A tungsten filament having a diameter of 0.1 mm. after having been purified by chemical methods and deprived of fat is caused to travel through a barium molybdate solution at the rate of about 35 cms. per minute, about 100 cms. of the filament being submerged in the solution. This filament is permanently connected With the negative pole of a source of current. The anode is formed by some suitable metal body, for instance a platinum body. A current of about 3 milliamp. is caused to flow through the solution. The filament leaving the solution which is coated with a blue layer of barium molybdenum bronze is rinsed with distilled water, dried in a current of hot air and placed on a reel. The filament thus prepared is mounted in a well known manner on the support of an electron tube and the cathode is then treated further preferably with metal vapor in a well known manner.

The solution of barium molybdate mentioned above can be produced for instance by precipitating barium metamolybdate from 1 litre of a sodium meta-molybdate solution by means of a watery solution of about 40 grams crystallized barium chloride. The barium meta-molybdate is filtered, washed with cold water and then suspended in 800 com. distilled water, so much dilute hydrochloric acid being added to the suspension that the barium meta-molybdate is dissolved. The solution is filled up with water to a volume of 1 litre.

Example 2 A molybdenum filament is first chemically purified and deprived of fat and. is then placed in a 10% barium meta-tungstate solution, heated to 80 0., the filament; being fully submerged in the solution and inserted in the electrolytic circuit as cathode, any metal body serving as anode. The electrolytic process is carried through with a current having a cathodic current density Dk=25 milliamp. per cmz. Thirty seconds after the circuit has been closed the filament is removed from the solution, rinsed with hot water and dried. The filament may now be activated as cathode in a tube by the well known metal vapor method, the tube being evacuated, sealed and alkaline earth metal vapor produced therein.

The cathode body or core may consist besides tungsten or molybdenum also of other metals having a correspondingly high melting point, such as for instance nickel.

Cathodes produced according to this method have been found to be very eificient, their electron emission being particularly powerful and persisting.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

I claim:-

1. As a new product an oxide cathode comprising a metal core, a coating on the surface of said core, of an alkaline earth metal compound known under the name of bronze, of a metal of the group of metals constituted by tungsten and molybdenum and a layer of an alkaline earth metal oxide on said coating.

2. As a new product an oxide cathode comprising a metal core a coating, on said core, of an alkaline earth metal tungsten bronze and a layer of an alkaline earth metal oxide on said coating.

3. As a new product an oxide cathode comprising a metal core, a coating, on said core, of an alkaline earth metal molybdenum bronze and a layer of an alkaline earth metal oxide on said coating.

4. The method of producing an oxide cathode comprising producing on a metal body serving as cathode core a layer of an alkaline earth metal compound, known under the name of bronze, of a metal of the group of metals constituted by tungsten and molybdenum and thereafter precipitating on this layer an alkaline earth metal from the Vapor phase.

5. The method of producing an oxide cathode comprising producing on a metal body serving as cathode core a layer of an alkaline earth metal tungsten bronze and molybdenum bronze and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

6. The method of producing an oxide cathode 5 comprising placing a metal body in a solution of barium meta-tungstate BaWeOrs-kQI-IzO, connecting said body as cathode in an electrolytic j circuit, causing the electrolytic current to act on the solution to deposit barium tungsten bronze on 10 the metal body, and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

7. The method of producing an oxide cathode comprising placing a metal body in a solution of barium metatungstate BaW4013+9H20, connecting said body as cathode in an electrolytic circuit, causing the electrolytic current to act on the solution to deposit on the metal body a layer of barium tungsten bronze and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

8. The method of producing an oxide cathode comprising precipitating by electrolytic decomposition a layer of a compound, known under the name of bronze, of a metal of the group of metals comprising tungsten and molybdenum, on a metal body forming the cathode placed in a solution of a salt of an acid of the group of acids constituted by metaand polytungstic and molybdic acids, 'and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

9. The method of producing an oxide cathode comprising placing a metal body forming the core of the cathode in a solution of an alkaline earth metal salt of an acid of the group of acids constituted by metaand polytungstic and molybdic acids, connecting said body as cathode in an electrolytic circuit, causing the electrolytic circuit to act on the solution to deposit on the metal body 40 by electrolytic decomposition a layer of a compound, known under the name of bronze, of a metal of the group of metals constituted by tungsten and molybdenum and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

10. The method of producing an oxide cathode comprising placing a metal body in a solution of a salt of an acid of the group of acids constituted by metaand polytungstic and molybdic acids, is

connecting said body as cathode in an electrolytic circuit, causing the electrolytic circuit to act on the solution to deposit on the metal body by electrolytic decomposition a layer of a compound,

known under the name of bronze, of a metal of the group of metals constituted by tungsten and molybdenum and thereafter precipitating on this layer an alkaline earth metal from the vapor phase.

11. The method of producing an oxide cathode comprising placing a metal body in a solution of a salt of an acid of the group of acids constituted by metaand polytungstic and molybdic acids, connecting said body as cathode in an electrolytic circuit, causing the electrolytic circuit to act on the solution to deposit on the metal body by electrolytic decomposition an alkaline earth metal compound of one of these acids, and thereafter precipitating on this deposit an alkaline earth metal from the vapor phase.

EMIL THEISZ. 

